需求

实现一个echo server。通俗的说就是客户端发送什么就会接受到什么。echo的意思“回声”。

服务端

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new ServerBootstrap()
               .group(new NioEventLoopGroup())
               .channel(NioServerSocketChannel.class)
               .childHandler(new ChannelInitializer<NioSocketChannel>() {
                   @Override
                   protected void initChannel(NioSocketChannel ch) {
                       ch.pipeline().addLast(new ChannelInboundHandlerAdapter(){
                           @Override
                           public void channelRead(ChannelHandlerContext ctx, Object msg) {
                               ByteBuf buffer = (ByteBuf) msg;
                               System.out.println(buffer.toString(Charset.defaultCharset()));

                               // 建议使用 ctx.alloc() 创建 ByteBuf
                               ByteBuf response = ctx.alloc().buffer();
                               response.writeBytes(buffer);
                               ctx.writeAndFlush(response);

                               // 思考：需要释放 buffer 吗
                               buffer.release();// 没有向后传递了，所以应该释放？
                               // 思考：需要释放 response 吗
                               response.release();// 没有向后传递了，所以应该释放？
                           }
                       });
                   }
               }).bind(8090);

客户端

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NioEventLoopGroup group = new NioEventLoopGroup();
       Channel channel = new Bootstrap()
               .group(group)
               .channel(NioSocketChannel.class)
               .handler(new ChannelInitializer<NioSocketChannel>() {
                   @Override
                   protected void initChannel(NioSocketChannel ch) throws Exception {
                       ch.pipeline().addLast(new StringEncoder());
                       ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
                           @Override
                           public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
                               ByteBuf buffer = (ByteBuf) msg;
                               System.out.println(buffer.toString(Charset.defaultCharset()));

                               // 思考：需要释放 buffer 吗
                               buffer.release();//可以释放。不释放，tail会释放。能自己释放还是自己释放。
                           }
                       });
                   }
               }).connect("127.0.0.1", 8090).sync().channel();
       channel.closeFuture().addListener(future -> {
           group.shutdownGracefully();
       });
       new Thread(() -> {
           Scanner scanner = new Scanner(System.in);
           while (true) {
               String line = scanner.nextLine();
               if ("q".equals(line)) {
                   channel.close();
                   break;
               }
               channel.writeAndFlush(line);
           }
       }).start();

运行结果

客户端打印输出

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hello
hello
hey
hey